Instrument for describing arcs of circles.



PATENTEDZSEPT. 17, 1907.

A. W. ALLEN. 1 INSTRUMENT FOR DESCRIBING ARCS 0F GIRGLES.

LPPLLOATIOFIILBD NAB. 18,1907.-

ALONZO W. ALLEN, OF STREATOR, ILLINOIS.

INSTRUMENT FOB DESCRIBING ARCS OF CIRCLES.

Specification of Letters Patent.

Patented Sept. 1'7, 1907.

Application filedMaroh 18,1907. Serial No. 382,959.

To all whom it may concern:

Be it known that I, ALoNzo W. ALLEN, a citizen of the United States, residing at Streator, in the county of Lasalle and State of Illinois, have invented new anduseiul Improvements in Instruments for Describ ing Arcs of Circles, of which the following is a specification.

My invention pertains to instruments for describing arcs of circles without the use of a central point; and it contemplates the provision of an instrument through the medium of which an arc of a circle may be eicpeditiously and easily drawn from a cord line and versine.

With the foregoing in mind, the invention will be fully understood from the following description and claims when the same are read in connection -with'the accompanying drawings, forming part of this specification, in which:

Figure 1 is a plan view illustrating the two members of my novel instrument as the same appear when properly arranged in the first instance relative to a cord line and a versine from which the arc of a circle is to be drawn. Fig. 2 is a detail view showing the marker-carrying member adjusted to put the marker at the top or upper end of the versine, in which position the marker is placed precedent to endwise move ment of the marker-carrying member to effect the drawing of the arc of a circle. Fig. 3 is a front elevation of the intermediate portion of the pencil-carrying member of the instrument. Fig. 4 is a rear elevation of the same. Fig. 5 is a transverse section taken in the plane indicated'by the line 55 of Fig. 1. Fig. 6 is a detail perspective view of the swinging end of one arm of the member against which the marker-carrying member bears.

Similar letters designate corresponding parts in all of the views of the drawings, referring to which:

A is the pencil-carrying member of my novel instrument, and B is the member which is designed to be adjustably fixed on a table or the like, and against which the member A is designed to bear and be moved.

As best shown in Fig. 1, the member A comprises two straight sections or arranged in the same horizontal plane and pivotally connected together through the medium of a threaded bolt b, an upright 0 having an apertured flange cl at its lower end, disposed above the sections a and receiving the bolt b, a thumb nut e mounted on bolt 1) above the flange d of upright c and having for its oifice to adjustably fix the sections a together and to adjustably fix the upright c with respect to the sections a, and a holderf of suitable construction carried by the upright c and adapted to receive a marker 9, preferably a pencil, as shown.

The member B is made up of arms in pivotally connected together at n in the manner shown or in any other manner compatible with the purpose of my invention. Each of the said arms m is provided at its free or swinging end with a flat pointed portion 10, arranged flush with its under side, and a pointed portion r arranged at about the distance shown in rear of the point p and designed to hear at its end against the rear edge of one section a of the marker carrying member A. Each arm in is also provided with a depending barb 8, designed to be embedded in a table top or other surface with a view offixing the arm on the surface and with respect to the other arm m. As shown in Fig. 1, the distance between the points of the arm portions 0 and the points of the arm portions r corresponds to the distance between the marker 1 and the rear edges of the connected portions of the sections a in member A for an important purpose presently set forth.

In the practical use of my novel instrument, the draftsman first determines and draws the cord line M and the versine N of the are that he is desirous of producing, and then opens the member B and fixes it in position with the points of its portions 10 located at the end of the cord line M. With this done, the draftsman places the sections a of member A on the portions p of member B and against the points of portions r, and then places the marker 1 on the versine N and' flexes the sections a so as to carry the marker to the top or upper end of the said versine. He then tightens the nut e, and slides the sections a against the points of the portions 1" on the arms of members B so as to carry the marker {1 from one end of the cord line M to the other, when, as will be readily understood, the marker will describe the are desired.

It will be apparent from the foregoing that through the medium of my novel instrument, a draftsman is The construction herein shown and described constitutes the preferred embodiment of my invention, but it is obvious that in practice various changes in the form, construction and relative arrangement of parts may be made without involving departure from the scope of my invention as defined in the claims appended.

Having described my invention, what I claim and desire to secure by Letters Patent, is:

1. In an instrument for the purpose described, a membercomprising two straight sections pivotally connected together and provided at a point adjacent to the point of connection with a marker; in combination with a member comprising two connected arms arranged to swing toward and from each other and having flat, pointedportions at their free ends adapted to rest under the sections of the first mentioned member and also having portions in rear of the flat, pointed portions, arranged to afford bearings for the rear edges of the sectionscomprised in the first mentioned member.

2. In an instrument for the purpose described, a memthe sections of the first mentioned member, and pointed ber comprising two straight sections arranged in the same portions located in rear of the flat, pointed portions, horizontal plane, a threaded bolt pivotally connecting said arranged to afford bearings for the rear edges of the secsections together, an upright carrying a marker-holder and tions comprised in the first mentioned member.

5 having an apertured base flange receiving the threaded In testimony whereof I have hereunto set my hand in 15 bolt, and a nut mounted on said bolt, above the base presence of two subscribing witnesses. flange; in combination with a member comprising two ALONZO W. ALLEN. connected arms arranged to swing toward and from each Witnesses: other and having depending barbs and also having flat, Cnsnnn Fosnnn,

10 pointed portions at their free ends adapted to rest under CHARLES CORRIGAN. 

